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R. ENGKE 81: 0'. PROLIGH. APPARATUS FOR ELEGTRQLY'IIG PRODUCTION OF ZINC.

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APPARATUS FOR ELECTROLYTIC PRODUCTION OF ZINC. No. 558,052; Patented Apr. 14, 1896.

' 5 W/ QWW M WW AN DREW BGRAHAM. PHOTO-LUNQWASHING'TOMDC UNITED STATES,

PATENT OEEIQE.

ROBERT ENCKE AND OSCAR FRGLICI'I, OF BERLIN, GERMANY, ASSIGNORS TO SIEMENS & I-IALSKE, OF SAME PLACE.

APPARATUS FOR ELECTROLYTIC PRODUCTION OF ZINC.

SPECIFICATION forming part of Letters Patent No. 558,052, dated April 14, 1896.

Application filed July 31, 1895. Serial No. 557,752. (No model.)

To all whom it may concern.-

Be it knownthat we, ROBERT ENOKE, a subject of the German Emperor, and OSCAR FRo- LIOH, a citizen of the Swiss Republic, both residing at Berlin, in the German Empire, have invented a certain new and useful Improved Apparatus for the Electrolytic Production of Zinc; and we do hereby declare the following to be afull, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

With the methods heretofore employed for efiecting the electrolysis of zinc solutions it has not generallybeen possible to realize such a profit as would admit of the process being considered technically valuable. The cause thereof has been the peculiar phenomenon that the zinc was separated in such a form that it could not be employed for technical purposes, for when the solutioncontains the least impurity there is deposited on the oathode not solid zinc, but instead thereof socalled zinc sponge -2' e. zinc in a fine noncohering powder of a dark color, which is only fusible with great difficulty, and consequently not practically workable.

Now it is a known fact that zinc sponge is mainly'produced when the solution is alkaline and contains other metals in addition to zinc. It occurs, however, also when the solution is decidedly acid and the impurities are nearly all removed. I

This invention relates to an improved apparatus by which even in the above-named extreme cases the formation of sponge can be entirely avoided.

It has been found that when a zinc lye of any degree of impurityis subjected to electrolysis tion of means for imparting an increased circulation to the liquid as compared with the speed heretofore employed, but that the action of the exceedingly high speed of circulation used depends upon some hitherto unknown molecular process in the electrolysis of zinc, which prevents the formation of zinc sponge. The said high speed of circulation can be carried out by any suitable meanssuch, for instance, as stirring apparatus. It has, however, been found most advantageous to effect the circulation by introducing com pressed air into the lye at the lower end of the vats, which, by its bubling up, produces the desired motion of the liquid. Experiments have shown that a solid zinc deposit is in many cases more easily obtained if the circulation of the electrolyte is effected by blowing in air instead of by other mechanical means. This fact is probably due to a chemical oxidizing action of the air upon the impurities of the electrolyte.

The said invention is preferably carried out by means of apparatus which will be described with reference to the accompanying drawings.

Figure 1 shows a diagrammatic view of the whole apparatus. Figs. 2, 3, and 4 show, respectively, a longitudinal section, cross-section, and plan of the bath.

In Fig. 1, Z Z are the cells in which the electrolysis is to be effected.

G is a source of electrical energy of any suitable kind, such as a dynamo actuated by a suitable motor M, such as a steam-engine, for producing the current required for the electrolysis, the current being supplied through conductors C O to the cells Z Z, which are here shown connected in series. The cells may, however, be arranged and connected in any other manner most suitable for each par-- ticular case. p

The motor M, in addition to driving the dynamo G, also drives a suitable air-compressing machine R, such as a Roots blower, for

The internal arrangement of the cells Z Z is shown at Figs. 2 and 3.

E E and E E are the electrodes, of which the cathodes E are preferably of zinc, while the anodes E are preferably of carbon, lead,

or other suitable bodies that are not materially attacked by oxygen.

The electrodes are supported in the cells in any approved manneras, for instance, by bands 70, secured to the electrodes and engaging with cross-barsk, resting on top of the cells.

On both sides of the electrodes, Fig. 3, are arranged wooden partitions H H, which do not quite reach up to the level of the liquid nor quite to the bottom. Into the compartments K K, formed behind these partitions, the

branches P of the air-pipe P descend to near the lower edges of the partitions H II and are there connected with horizontal pipes P provided with perforations.

The action of the apparatus is as follows:

The zinc contained in the natural ores is converted in the known manner by roasting into zinc oxide. It is then preferably dissolved out by means of sulfuric acid, and after being freed as much as possible, by any known purifying process, from any foreign metals contained in the solution, it is led into the cells Z Z. The motor M is at the same time made to actuate the current-producer G and the Roots blower R, so that the zinc solution is subject to electrolysis, while air is forced by the Roots blower through the pipe P and branches P into the compartments, in the lower part of which it issues through the perforations of the pipe P I11 consequence of the upward currents thus produced the liquid will be made to rise in each compartment and will flow continuously over the upper edge of thewood partitions H H into the middle space of the cell in which the electrolytic action takes place. By this means a downward current of the electrolyte is produced, flowing along the electrode-plates E E and E E, to which current any desired velocity can be given between practical limits by suitable adjustment of the supply of air under pressure. The air is injected in sufficient quantity and at a sufficient pressure to cause the liquid over the air-holes to rise from two to five centimeters above the adjacent liquid. lVhen circulated against the minimum head of two centimeters, the theoretical velocity of the circulating liquid is about thirty feet a minute.

Naturally the speed of circulation should be chosen vas small as possible, because an increase in the speed of circulation entails an increase in the power absorbed. On the other hand, the speed of circulation must be increased so far that the zinc is separated from the electrolyte, not as zinc sponge, but as a solid deposit on the cathode.

By way of example it may be stated that good results will generally be obtained if with a current density of about fifty amperes to the square meter of the cathode surface and with cathodes of about one meter length and 0.7 meter width an air-current equal to about 1.3 cubic meter per hour for each cathode is employed.

In employing with the above proportionsa zinc-sulfate lye of about 10 Baum and an acidulation of about five to ten grams of free sulfuric acid per liter, the formation of sponge will be avoided and a fine solid deposit be obtained, even in the presence of the most diverse impurities, of which, however, the greater portion is assumed to have been previously removed.

The electrolysis is effected in such manner that zinc is deposited on the cathodes while oxygen is set free at the anodes. The volume of the lye contained in the electrolytic apparatus remains constant, with the exception of small losses. It circulates continuously between the electrolytic apparatus and the lixiviation vessels.

In passing through the electrolytic apparatus the percentage of acid in the lye is increased and the percentage of zinc is diminished. On passing through the lixiviation vessels the percentage of acid is decreased and that of the zinc is increased, so that the mean composition of the lye is constant.

It has been found, further, that the way in which free sulfuric acid is produced in the depositing-vats has an influence on the formation of zinc sponge. If the acid is added to the lye, zinc sponge is formed under some circumstances even when the acid is chemically pure. If, on the other hand, the free acid is produced by taking in the first instance neutral lye and by depositing zinc from it until the wished-for degree of acidity is reached, without regenerating the lye with zinc oxide, the formation of zinc sponge is obviated. As in this initial process zinc sponge may be formed, the cathodes, after the standard degree of acidity has been reached, are cleaned from the zinc sponge, and subsequently the special regular process commences, in which the acid formed in the depositing-vats is fixed by dissolving zinc oxide.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is-- 1. The combination, with an electrolytic cell, and the anodes and cathodes supported crosswise therein, of partition-plates extending lengthwise of the cell, spaces being left above and below the said plates for the electrolyte to circulate; and air-pipes provided with perforated portions arranged near the bottom of the cell between its sides and the said plates, whereby the electrolyte is caused to circulate around the said plates, substantially as set forth.

2. The combination, with an electrolytic cell, and electrodes supported therein; of partition-plates arranged substantially vertical In testimony whereof We have affixed our in the cell, spaces being left above and below signatures in presence of two Witnesses.

the said plates for the passage of the electro- ROBERT ENOKE.

lyte; and means for circulating the electro- OSCAR FROLIOH. 5 lyte at a high velocity around the said plates WVitnesses:

and over the electrodes, substantially as set EMIL KOLLINER,

forth. MAX WAGNER. 

